Facilitated Diffusion Involves Passive Protein-Mediated Transport

Steps:

• Recall that facilitated diffusion is a passive process moving substances down their concentration gradient without energy input.
• Identify that it requires proteins like channels (open pores) or carriers (bind and flip substances) to aid polar or large molecules.
• Eliminate options mentioning energy use, as that's active transport, not diffusion.
• Confirm the correct description matches protein use without energy or shape change mandates.

Why B is correct:

• Facilitated diffusion definition states it uses channel or carrier proteins for passive movement down gradients, with carriers changing shape but channels not always doing so.

Why the others are wrong:

• A: Incorrectly requires energy and shape changes, confusing it with active transport.
• C: Wrongly includes energy use, which defines active transport, not passive diffusion.
• D: Falsely describes gradient creation and opposite ion movement, which is active transport like the sodium-potassium pump.

Final answer: B